MongoDB Query to Find All Documents

Use db.collection.find({}) to find all documents in a MongoDB collection; the empty curly braces {} mean no filter is applied.

Examples

Inputdb.users.find({})

Output[{ "_id": 1, "name": "Alice" }, { "_id": 2, "name": "Bob" }]

Inputdb.products.find({})

Output[{ "_id": 101, "item": "Pen" }, { "_id": 102, "item": "Notebook" }]

Inputdb.emptyCollection.find({})

Output[]

How to Think About It

To find all documents, think of it like asking for every item in a box without any condition. In MongoDB, the find method retrieves documents, and passing an empty object {} means no filtering, so it returns everything.

Algorithm

1

Identify the collection you want to search.

2

Use the <code>find</code> method on that collection.

3

Pass an empty object <code>{}</code> as the filter to select all documents.

4

Execute the query to get all documents.

5

Return the list of documents found.

Code

mongodb

const allDocuments = await db.collection('myCollection').find({}).toArray();
printjson(allDocuments);

Output

[
  { "_id": ObjectId("..."), "field1": "value1" },
  { "_id": ObjectId("..."), "field2": "value2" }
]

Dry Run

Let's trace finding all documents in the 'users' collection.

1

Call find with empty filter

db.users.find({}) means select all documents because filter is empty.

2

Retrieve documents

MongoDB returns all documents like [{_id:1, name:'Alice'}, {_id:2, name:'Bob'}].

Step	Action
1	find({}) called with empty filter
2	All documents returned

Why This Works

Step 1: Empty filter means no restriction

Passing {} to find tells MongoDB to not filter out any documents.

Step 2: find returns a cursor

find returns a cursor to iterate over all matching documents.

Step 3: Convert cursor to array

Using toArray() collects all documents into a list for easy use.

Alternative Approaches

Using find with projection

mongodb

db.collection.find({}, { _id: 0, name: 1 }).toArray();

Returns all documents but only shows the 'name' field, hiding others.

Using findOne in a loop (legacy)

mongodb

let doc = db.collection.findOne({}); while(doc) { printjson(doc); doc = db.collection.findOne({_id: {$gt: doc._id}}); }

Less efficient and more complex; not recommended for simply getting all documents.

Complexity: O(n) time, O(n) space

Time Complexity

The query scans all documents in the collection, so time grows linearly with the number of documents.

Space Complexity

Storing all documents in memory requires space proportional to the number of documents returned.

Which Approach is Fastest?

Using find({}) with no projection is fastest for retrieving all documents; adding projections or looping manually adds overhead.

Approach	Time	Space	Best For
find({})	O(n)	O(n)	Getting all documents quickly
find({}, projection)	O(n)	O(n)	Getting specific fields only
findOne loop	O(n^2)	O(1)	Legacy, inefficient for all documents